Abstracts Brochure - CERN

TUPCH — Poster Session 27-Jun-06 16:00 - 18:00
functions. A client application can have access to the server data using the DOOCS application programming interface.
A set of generic and specially devoted programs provide the tools for the operators to control the RF system.
The RF operation at the linac is being automated by the implementation of DOOCS finite state machine servers.
Phase and Amplitude Stability of the Next Generation RF Field Control for VUV- and Xray
Free Electron Laser
For pump and probe experiments at VUVand
X-ray free electron lasers the stability of F. Ludwig, M. Hoffmann, H. Schlarb, S. Simrock (DESY)
the electron beam and timing reference must
be guaranteed in phase for the injector and bunch compression section within a resolution of 0.01 degree (rms) and in
amplitude within 1 10-4 (rms). The performance of the field detection and regulation of the acceleration RF directly
influences the phase and amplitude stability. In this paper we present the phase noise budget for a RF-regulation
system including the noise characterization of all subcomponents, in detail down-converter, ADC sampling, vectormodulator,
master oscillator and klystron. We study the amplitude to phase noise conversion for a detuned cavity.
In addition we investigate the beam jitter induced by these noise sources within the regulation and determine the
optimal controller gain. We acknowledge financial support by DESY Hamburg and the EUROFEL project.
FPGA-based RF Field Control at the Photocathode RF Gun of the DESY VUV-FEL
At the DESY Vacuum Ultraviolet Free Electron
Laser (VUV-FEL) bunch peak current E. Vogel, W. Koprek, P. Pucyk (DESY)
and the SASE effect are (amongst other parameters)
sensitive to beam energy and beam phase variations. The electron bunches are created in an rf gun, which
does not have field probes. Variations of the gun rf field cause beam energy and phase variations. They have a
significant influence on the overall performance of the facility. DSP based rf field control used previously was only
able to stabilize the rf output of the klystron. This was due to the lack of processing power and the over-all loop delay.
The controller was not able to provide satisfactory rf field stability in the gun. Replacing the DSP hardware by the
new FPGA-based hardware Simulation Controller (SimCon), we are able to reduce the latency within the digital part
significantly allowing for higher loop gain. Furthermore SimCon provides sufficient processing power for calculating
a probe signal from the forward and reflected power as input for PI and adaptive feed forward (AFF) control. In this
paper we describe the algorithms implemented and the gun rf field stability obtained.
Universal Controller for Digital RF Control
Digital RF control systems allow to change
the type of controller by programming of the S. Simrock (DESY) M.K. Grecki, G.W. Jablonski (TUL-DMCS)
algorithms executed in FPGAs and/or DSPs.
It is even possible to design a universal controller where the controller mode is selected by change of parameters. The
concept of a universal controller includes the self-excited-loop (SEL) and generator driven resonator (GDR) concept,
the choice of I/Q and amplitude or phase control, and allows for different filters (including Kalman filter and method
of optimal controller synthesis) to be applied. Even time-varying mixtures of these modes are possible. Presented is
the implementation of such a controller and the operational results with a superconducting cavity.
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